The invention relates to a method of treating metal melts with flush gas during continuous casting, wherein the molten metal is led from a tundish having an outflow opening and, if desired, a casting tube, into a mould, as well as to an apparatus for carrying out this method.
Generally speaking, continuosly cast slabs have a very uniform quality over their entire lengths. In some areas, however, there may be local quality deteriorations due to the pollution of the edge zone by slag inclusions which pollution would lead to high scarfing losses. Such quality changes may, among other things, be caused by a lowered level of the bath in the tundish.
If the casting level in the tundish falls below a certian level, suction and eddies form in the outlet area that are so strong that the covering slag floating on the metal bath together with liberated inclusions, is sucked into the casting tube and gets into the strand. This critical level of the bath depends on the amount of steel flowing out per time unit. When the casting performance is increased, e.g. 3.0 metric tons/minute, suction phenomena may occur up to a casting level height of 300 mm.
Although attempts are made to keep the level of the bath as high as possible during the whole casting procedure, the level of the bath cannot be prevented from sinking from time to time. Such a sinking will occur, e.g. when the outlet of the casting ladle narrows, when ladle outlets must be burnt out, when the ferrostatic pressure in the casting ladle decreases towards the end of casting, when samples are taken from the casting stream and when successive castings are carried out during the exchange of the ladle.